Enclosure-in-Chamber Setup to Achieve Near-Zero Background Concentrations for Brake Emissions Testing

Measuring brake emission continues to be a challenging non-standardized task. Extensive research is ongoing and as seen in the work in progress presented at SAE Brake Colloquium and PMP meetings. However, open items include how to achieve lower background concentration and how to design the brake enclosure. A low background concentration is essential as brake events are short and some emissions are in the range of reported background levels. Hence these emissions are difficult to distinguish from the background level. Even more critical, a high background concentration can result in a wrong particle number emissions value, either overestimated, background counted as emissions, or underestimated, background level subtracted, and low emission events no longer detected and counted. Reducing the background level to less than 100 #/cm³ appeared to be quite challenging. Applying experience in validating automotive air filters and in industrial HVAC filters, an enclosure-in-chamber setup was developed. The concept was adapted and implemented for the LINK 3900 dynamometer as for the outer chamber. The brake itself is placed in a rectangular enclosure with easy access to. Key enabler for a background level close to zero is the individual control of the inlet and outlet flow rates to this inner enclosure and an additional H13 air filter besides other (sealing) measures. The (outer) chamber of the LINK 3900 is run at negative pressure, to prevent emissions into the workplace, and the inner enclosure of the brake has a slight positive pressure to avoid particle intake through the gaps. The setup is presented in detail, including particle measurement (PM and PN) as used for measurements at LINK Limburg, Germany. This work discusses the results showing a background concentration of less than 10 #/cm³ measured with a TSI CPC 3756. This low level of background concentration is stable over the entire cycle time and has been observed for WLTP exhaust as well as the Novel braking cycle (WLTP- Brake Cycle).